FIG. 11 shows a step in the manufacture of a spar or beam of composite material with a double T cross section, according to a conventional method. The spar is initially assembled in an uncured state, by bringing together the webs of two profiled components 15, 16 with cross sections in the form of opposed C-shapes. Fillers F of carbon fibre and/or structural adhesive, with a pseudo-triangular cross section, are then applied along the longitudinal recesses R which are present along the junction areas between the webs and flanges of the two profiled sections.
Problems have arisen concerning the quality of the junction areas (or “radial” areas) of the spars, owing to the geometrical imprecision of the fresh (uncured) fillers. The imprecision may be due to the filler production process, which is usually carried out by vacuum forming or extrusion. Conventional fillers cannot repeatedly provide the geometrical precision (in terms of radii and thicknesses) specified on the drawings of components which are to be cured on the filler. In other cases, the imprecision may be seen after the step of co-curing with the other components of the spar, with the appearance of wrinkles, accumulations of resin (called “resin pockets”) and fibre distortion. This has led to an increase in rejects, repairs and structural operations in support of the evaluation of the acceptability of the various types of defects encountered.
Moreover, the presence of fillers in the nodes of beams makes it difficult to inspect the radial areas of the spars with ultrasonic methods, since it disperses the signal.
The filler is an integral part of the beam or spar. Its use is dictated by the need to fill the cavity in the junction area to enable the radii of the spars to be compacted correctly during the autoclave curing, which takes place under pressure in vacuum bags. The filler provides a “support” or “reaction” function without which the beam would collapse in the radial area under the action of the pressure of the autoclave and the vacuum bag. The reactive force exerted by the filler also allows correct curing of the C-section profiled components in the radial area, thereby ensuring the absence of porosity.